Drill strings are prone to become stuck in the earth boreholes as drilling progresses. The mode of sticking addressed by this invention usually involves the drill collars used for ballast above a drill bit. Three mechanisms for sticking will be defined as typical. First, certain formations swell when exposed to some drilling fluids. The hole simply closes in on the drill string. Second, some formations behave as filters and draw liquid out of drilling fluid to continually add solids as coating to the bore hole wall. The hole effectively shrinks in this process. Third, there is usually a pressure difference between liquid in the bore and fluids in the formation. This in effect applies a suction to the drill collar surfaces in contact with the borehole wall. This is called "differential sticking."
To reduce the tendency for differential sticking, spiral grooves have been milled in drill collars. This helped pressure equalize around the drill collar periphery and was quite beneficial in many cases.
The U.S. Pat. No. 3,804,186 taught the use of holes (or jets) through the drill collar wall to permit fluid to be ejected radially against the bore wall to reduce the tendency for the collars to stick. The fluid could be applied to the collar wall jets by rotating the drill string backward to actuate a selector valve to close off the usual drilling fluid route through a drill bit and divert the fluid to the collar wall jets.
There is considerable reluctance in the oil drilling industry to rotate a drill string backward, because of the tendency of the drill string to disconnect at unpredictable locations. Additionally, the valve mechanism is effectively a free motion element, and some drilling situations are so severe as to develop weakness in any free motion element. Better methods of valve actuation are needed. My copending patent application for a Remote Controlled Selector Valve offers an improved combination.